This collection consists of lab notebooks, photomicrographs, a nd a summary report produced by Geophysical Laboratory staff member s in the course of carrying out research on various topics related to machine gun barre ls during World War II. The work was carried out at the Geophysical La boratorys former location on Upton Street NW in Washington, DC, as well as at Naval testing sites at Carderock and Indian Head, Maryland. The Geophysical Laboratorys share of this work, under contract to the NDRC a nd in parallel with teams at the National Bureau of Standards, the Crane Company of Chicago, and the Research and Development Division of Army Ordnance, concerned the erosion of m achine gun barrels by the gases produced during firing, and the identification of alloys and the development of barrel lin ings to mitigate the damage caused by those gases. Experiments fo cused on the .50 caliber aircraft machine gun, whose barrel suffered from a high failure rate du ring periods of heavy fi re. Different linings, claddings, alloys, and bore desi gns were repeatedly test-fired, and the results analyzed, between 1941 and 1945.